1. Field of the Invention
The present invention relates to an apparatus and method for determining the tendency of liquid hydrocarbon streams to foul equipment and more particularly to an apparatus and method for determining oil-asphaltenes incompatibility and related fouling tendency.
2. Related Art
Petroleum streams, depending on their asphaltene and oil characteristics, have different precipitating and fouling characteristics with regard to heated oil refinery surfaces. The problem of predicting the offending substances in a particular stream such as crude oil which foul heat exchanger equipment in oil refineries and petrochemical plants has been virtually unresolved. Equipment fouling by heated hydrocarbon streams which result in inorganic and carbonaceous deposits on heat exchanger surfaces leads to a blockage of flow and a decrease in heat transfer. Both conditions severely reduce heat efficiency in the processing of the crude oil. A reliable technique for identifying the problem crudes would enable the operator to apply remedial measures such as removing the offending substances or by adding antifouling agents.
There are a number of methods and devices available for determining the rates of fouling of petroleum streams. Conceptually, they are all similar in that they attempt to measure the change in heat transfer from a heated surface to a test fluid. These methods are either not reliable or are time consuming.
One approach is to use a test unit which is designed to allow measurement of the fluid temperature at the exit of the heat-exchanger while the metal temperature of the heated tube is controlled. This configuration provides for close simulation of refinery and petrochemical plant heat-exchanger operations and provides for measurement of the significant effect of fouling which is indicated by the reduction of heat transfer. The test unit provides for a thermal fouling evaluation of the crude oil in an accelerated test which is designed to reproduce the fouling problem experienced in a refinery over several months. Acceleration is provided by carrying out test operating temperatures higher than those in a particular refinery unit, so that the prospective level of fouling can be produced in a reasonable period of time (usually 3-4 hours). Heat transfer data is obtained by holding the heater tube at a constant temperature while measuring the change in the liquid outlet temperature. As fouling progresses, i.e., a carbonaceous deposits build up on the heater tube surface, a decrease in the fluid outlet temperature results when using a constant outlet liquid temperature operation. The change in liquid outlet temperature with time provides the basic heat data required for comparative evaluation of untreated material and additive-treated material. The rate of change in outlet liquid temperature versus time shows relative fouling tendencies.
Current test equipment is only capable of measuring the overall tendency of heated petroleum stream to foul refinery equipment and cannot predict which are the offending substances or fractions.
An article entitled "Thin-Layer Chromatographic Method for Determination of Asphaltene Content of Crude Oils and Bitumens", authored by Poirer and George, published in 1983 Energy Sources, Volume 7, No. 1, discloses a method which involves determination of asphaltenes content by conventional thin-layer chromatographic (TLC) procedures, extraction of the asphaltenes by toluene, and colorimetric determination of the asphaltenes. This process involves the use of TLC tank with developer solvent. Although described as a fast method , the article states that about 8 hours are required to analyze 15 samples.
Hence, it is an advantage of the present invention that an improved method and apparatus which will rapidly indicate the fouling tendency of asphaltene containing petroleum streams is provided. It is a particular advantage the present invention can be employed in the refinery in a very short period of time by unit operators without extensive chemical training. These and other advantages and features will be apparent from the following test.